U.S. patent application number 09/826616 was filed with the patent office on 2002-10-10 for inspecting print quality using digital watermarks.
Invention is credited to Anglin, Hugh.
Application Number | 20020146120 09/826616 |
Document ID | / |
Family ID | 25247078 |
Filed Date | 2002-10-10 |
United States Patent
Application |
20020146120 |
Kind Code |
A1 |
Anglin, Hugh |
October 10, 2002 |
Inspecting print quality using digital watermarks
Abstract
An automatic label inspection system that is relatively
inexpensive, flexible and easy to set up. A digital watermark is
embedded in a label prior to the printing process. As is
conventional in digital watermark technology, the digital watermark
is duplicated many times in multiple areas of the image. That is,
the images is divided into area and a copy of the watermark is
embedded into each area. Conventional digital watermarks often
include both a grid and a payload signal. The present invention
merely requires use of the watermark grid signal. A label is
inspected by reading the watermark grid signal from each area of
the image. The strength of the watermark grid signal is used as a
measure of the quality of the label.
Inventors: |
Anglin, Hugh; (Claremore,
OK) |
Correspondence
Address: |
ELMER GALBI
13314 VERMEER DRIVE
LAKE OSWEGO
OR
97035
|
Family ID: |
25247078 |
Appl. No.: |
09/826616 |
Filed: |
April 5, 2001 |
Current U.S.
Class: |
380/54 |
Current CPC
Class: |
G06T 2201/0202 20130101;
G06T 1/0028 20130101; G06T 1/0071 20130101 |
Class at
Publication: |
380/54 |
International
Class: |
G09C 005/00 |
Claims
I claim:
1. A method of determining if a printing process operated correctly
comprising the steps of: digitally watermarking an image, said
watermark being redundantly applied in multiple areas of said
image, printing said image on a carrier, acquiring a second image
of the image printed on said carrier, reading the digital watermark
data from each area of said second image, determining the quality
of the printing from the acquired digital watermark data.
2. The method recited in claim 1 wherein said watermark includes a
grid signal.
3. The method recited in claim 1 wherein said carrier is a
label.
4. The method recited in claim 1 wherein said second image is
acquired using a digital camera.
5. The method recited in claim 3 wherein said label is rejected if
said digital watermark data does not meet certain criteria.
6. The method recited in claim 1 wherein quality is deemed
unacceptable if digital watermark data can not be read from each
area of said second image.
7. The method recited in claim 2 wherein said quality is deemed
unacceptable if said grid signal can not be read from each area of
said image.
8. A method of determining the quality of a printed image
comprising the steps of: digitally modifying said first image to
embed a digital watermark in said image, printing said first image
onto a carrier to create a printed image, acquiring a second image
of said printed image, reading said watermark from said second
image to generate watermark data, and determining the quality of
said printing from said watermark data.
9. The method recited in claim 8 wherein said carrier is a
label.
10. The method recited in claim 8 wherein said watermark comprises
a grid signal.
11. The method recited in claim 8 wherein said watermark includes a
grid signal.
12. The method recited in claim 8 wherein said watermark is
redundantly embedded in multiple areas of said image.
13. The method recited in claim 12 wherein said carrier is a
label.
14. The method recited in claim 13 wherein said label is rejected
if said watermark can not be read from at least one area of said
label.
15. A system for determining the quality of a printed image, said
printed image including a digital watermark, said watermark being
redundantly applied to multiple areas of said printed image, said
system comprising, an image capture device for acquiring a second
image of said printed image, a watermark reading program for
reading watermark information from each of said areas of said
image, examining the magnitude of watermark information to
determine the quality of said printing.
16. The system recited in claim 16 wherein said digital watermark
includes a grid signal.
17. A system for determining if the quality of printed labels is
acceptable, said labels being printed with an image which includes
a digital watermark embedded in multiple areas of said image, means
for acquiring an image of said labels after said labels have been
printed, means for reading watermark data from each area of said
image of said labels, means for indicating that the quality of said
labels is unacceptable if the watermark data read from each area of
said image does not meet specified criteria.
18. The system recited in claim 17 wherein said digital watermark
includes a grid signal.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to label printing and more
particularly to inspecting printed labels.
BACKGROUND OF THE INVENTION
[0002] In many manufacturing operations, labels are applied to
products or packages at very high speed. It is very important for a
variety of reasons that the labels be printed correctly and that
they be applied correctly. Among the reasons are the fact that the
labels create a product image and the fact that some labels contain
notices that are required for legal reasons.
[0003] Automatic label inspection using machine vision is possible.
However, labels often use colors and materials which make it
difficult if not impossible to effectively inspect labels using
relatively simple binary or gray scale inspection technologies.
Presently in some situations, colored labels are automatically
inspected using a "golden template". With such systems an image of
the label acquired by a machine vision system. The acquired image
is then automatically compared to the golden template. Various
known computerized image correlation techniques can determine if
the quality of the acquired image matches established the "golden
template".
[0004] In general, prior art automatic label inspection systems are
expensive and difficult to maintain. Furthermore existing automatic
label inspection systems often involve time consuming set up
processes for each new label. Often the set up process requires a
high degree of technical expertise.
[0005] The present invention is direct to providing an providing an
improved lable inspection system.
SUMMARY OF THE PRESENT INVENTION
[0006] The present invention provides an automatic label inspection
system that is relatively inexpensive, flexible and easy to set up.
The system and method of the present invention utilizes digital
watermarks. With the present invention a digital watermark is
embedded in a label. As is conventional in watermark technologyh,
the digital watermark is duplicated many times in the image. That
is, the image printed on the label is divided into areas and a copy
of the watermark is embedded into each area. Conventional digital
watermarks often include both a grid and a payload signal. The
present invention merely requires use of the watermark grid signal.
A label is inspected by reading the watermark grid signal from each
area of the image. The strength of the watermark grid signal in
each area is used as a measure of the quality of the printing on
the label in that area.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 illustrates a label divided into areas.
[0008] FIG. 2 is a block diagram of a system used to practice the
invention.
[0009] FIG. 3 and 4 illustrate examples of where the grid signal
was detected in the image of two different labels.
[0010] FIG. 5 is a block flow diagram of the operation of the
invention.
DETAILED DESCRIPTION
[0011] The present invention utilizes existing digital watermark
detection and reading technology such as that described in U.S.
Pat. Nos. 5,636,292, 5,710,834, 5,721,788, 5,748,783, 5,768,426,
5,841,978 or 6,122,403 all of which are hereby incorporated herein
by reference. With the present invention, digital watermarking
technology is applied to automatically inspect and determine the
quality of printing on a label.
[0012] The term label as used herein means any printed image or
text that appears on a package or item. The printed image can
include text and graphic material or pictures. A label can be a
relatively small such as the type of label that provides a notice
required by the FDA on a medicine bottles A label may be relatively
large such as the label that would appear on the side of a box
containing a refrigerator. A label may be glued to an item or it
can be text and graphic material printed on a box such as the text
and images that appear on many cereal boxes. A label consists of an
image printed on a carrier. The carrier can be paper, cardboard or
plastic.
[0013] Labels are used to provide information and/or an appealing
image to consumers. In may cases labels carry important
information. During manufacturing operations, there is a need and
desire to quickly and effectively check the quality of the printing
on a label and to insure that a label has in fact been correctly
placed on an item.
[0014] Known watermark technology such as that described in the
above referenced patents, utilizes a watermark that has both a grid
and a payload or data signal. The present invention merely requires
the use of a digital watermark that includes a grid signal.
However, a digital watermark that includes both a grid and a
payload signal can also be utilized to carry other useful
information as described later with respect to alternate
embodiments of the invention.
[0015] FIG. 1 illustrates a printed label. A watermark is
redundantly embedded into the image. It is noted that the label has
some background coloring into which a watermark can be embedded.
The label shown in FIG. 1 may be a gray scale or a multicolor
image. The technology for embedding watermark into such images is
well known. The shapes such as 102 merely indicate that the label
includes the type of graphic that is conventionally on labels. The
lines 105 indicate that the label includes textual material.
[0016] The doted lines in FIG. 1 which divide the image into a
number of square areas illustrate the fact that the image is
divided into areas and the watermark is redundantly embedded into
each of the areas in the image. The typical image would be divided
in areas, the size of which, would be in the order of one hundred
or two hundred pixels square. The lines in FIG. 1 merely illustrate
that there are multiple areas into which the watermark in
embedded.
[0017] FIG. 2 illustrates a system for practicing the present
invention. A package 201 moves along a conveyor 202. The package
201 includes a label 210. A camera 211 captures an image of the
label 210 and sends the image to a computer 250. The computer 250
includes a conventional operating system (such as for example the
Microsoft Widows operating system) and a watermark reading program
251. The output of the watermark reading program 251 goes to a
comparison program 252 which compares the grid signal in each area
to acceptable limits. The camera 211 can be a conventional digital
camera. It is noted that in alternative embodiments, instead of
using a computer with an operating system such as Microsoft
Windows, the computer 250 is what is termed an "embedded system"
program to perform the required tasks and camera 211 can be an
analog camera with a suitable capture card.
[0018] Examples of the result are shown in FIGS. 3 and 4. In the
example given in FIG. 3, the grid signal is detected in each tile
in which the watermark is embedded. Hence, the detected results
indicate that the label was printed correctly. In the example given
in FIG. 4, in four of the tiles, no grid signal was detected.
Hence, the results indicate that this label was not printed
correctly.
[0019] In alternative embodiments, algorithms which determine
pass/fail criteria based on neighborhood operations are used. For
example, a week grid signal in one tile might be acceptable if
there were a strong signal in all surrounding (neighboring) tiles.
In other alternative embodiments, morphological algorithms are
employed to perform erosions, dilations, openings and closings,
etc. Furthermore, blob labeling with ensuing feature extraction
could be used to find moment data for qualifying defects.
[0020] If a label does not meet the required criteria it is deemed
unacceptable. In such a case the package with the unacceptable
label is either appropriately marked for re-labeling or the package
is removed from the conveyor for further processing which can for
example include re-labeling the package.
[0021] The flow diagram in FIG. 5 illustrates how the invention
operates. The process begins with an image of a label. The image is
in digital form. The initial image can either be designed in
digital form (as is often done) or a physical label can be scanned
to create a digital image. As indicated by block 501, the image of
the label is watermarked. This can be done with a conventional
watermarking program. During the watermarking operation a grid
signal is embedded in each area of the image. That is, the grid
signal is redundantly embedded in multiple areas of the image. This
grid signal is embedded in the image by modifying the pixels of the
image to embed specific spatial frequencies in the image. The
changes done to embed these spatial frequencies are such that they
can not be recognized by a human observer; however, they can be
detected by a watermark reading program. Embedding selected special
frequencies in an image can be done with conventional watermarking
technology.
[0022] As indicated by block 503, the digital image is printed onto
a carrier ( i.e. on a physical label) and the physical label is
applied to a package. The image can be printed on the carrier (i.e.
on the physical label) and the physical label can be applied to the
product in the conventional manner.
[0023] Next as indicated by block 505 the labels are passed by a
digital cameras and an image of the label is acquired. The
watermark is next read from the acquired image as indicated by
block 507. Reading the watermark involves determining what spatial
frequencies appear in each area of the watermark. This operation is
done in a conventional manner. Next as indicated by block 509, a
determination is made as to whether the spatial frequencies that
represent a grid signal are present in each area of the image. That
is a determination is made as to which areas of the acquired image
include the grid signal. The result of this operation is data such
as that shown in FIGS. 3 and 4, the image. This can be a simple
"yes" no type of operation, or it can take into account the
magnitude of the various frequencies. In any event the frequency
spectrum of image the signal is examined to determine if there is a
watermark grid signal in each area of the image.
[0024] If there is no grid signal in an area where there should be
a grid signal, the label is rejected. Alternatively, if the
magnitude of the grid signal in a particular are is below a preset
threshold the label is rejected.
[0025] Naturally on some labels area of the label are blank, hence,
one would not expect to find a signal in these areas and these
selected area are ignored. With many existing watermark reading
program the first step performed by the program is to determine if
the image has been enlarged or rotated. With this application of
digital watermark technology, those steps are not necessary, since
the size of the acquired image is fixed and the location of the
tiles where the watermark is embedded is known. However, if the
speed of the convey is such that synchronization is not easily
possible, the conventional steps used to locate area where a
watermark is located could be used.
[0026] It is noted that the present invention also can be used to
detect if a label is in fact present on a package. If for example,
a label is misplaced, or if a label is not present on a package,
the watermark reading program would not detect a grid signal.
[0027] While the embodiments of the invention described above
utilize a conventional watermark grid signal, specialized watermark
signals could be developed which in some situations would provide a
better quality measurement for labels. Furthermore, in alternative
embodiments of the invention, in addition to containing a grid
signal, the watermark could contain other data. For example, the
watermark could include data which allows someone to link to a web
site using the technology described in PCT publication WO 00/70585
published Nov. 23, 2000 and entitled "Methods and Systems for
Controlling Computers or Linking to the Internet Resources from
Physical and Electronic Objects". His publication is hereby
incorporated herein by reference. Thus the label inspection process
according to the present invention could utilize a digital
watermark that is placed on the label for other purposes such as
for allowing a consumer to link to a web site. While the invention
has been described with respect to preferred embodiments of the
invention, it should be understood that various changes in form and
detail may be made without departing from the spirit and scope of
the invention. Applicant's invention is limited only by the
appended claims.
* * * * *